There is not a single "the cable" to cut. Some people get Internet access from the Cable TV company, some from the phone company, some from satellite providers, but I'd dare say most of these people are accessing Facebook via their smart phones. The smart phone also removes the possibility of a power outage making their using Facebook impossible - they should have it for at least a couple of hourss.
I'd also doubt anyone sophisticated enough to hack their private instant messaging would be associating with the idiots who break into houses as a source of income.
Other than that, I agree with you about a neighborhood watch but I'm sure they're doing that too.
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